Implantable medical device configured as a pedometer

ABSTRACT

A system includes an implantable medical device. The implantable medical device includes a control circuit and a motion sensing device. The motion sensing device is coupled to the control circuit, and the motion sensing device is configured to transmit signals to the control circuit. The control circuit is configured to identify one or more steps of a patient using the motion sensing device signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. Application Ser. No.11/733,663, filed on Apr. 10, 2007, now issued as U.S. Pat. No.7,844,336, the benefit of priority of which is claimed herein, and whichis incorporated herein by reference in its entirety.

TECHNICAL FIELD

This document pertains generally to implantable medical devices, andmore particularly, but not by way of limitation, to implantable medicaldevices configured as a pedometer.

BACKGROUND

Implantable medical devices include, among other devices, cardiac rhythmmanagement devices. Such implantable medical devices can include amotion sensing device such as an accelerometer, a tilt switch, or amercury switch, and the motion sensing device can be used to detect andmonitor the physical activity of a patient. This physical activity datahas been used to modulate a pacing rate as a function of a patient'sphysical activity. However, many times the activity data generated by amotion sensing device associated with an implantable medical device iscryptic and difficult to interpret.

OVERVIEW

This overview is intended to provide an overview of the subject matterof the present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the subjectmatter of the present patent application.

In Example 1, a system includes an implantable medical device. Theimplantable medical device includes a control circuit and a motionsensing device, coupled to the control circuit, the motion sensingdevice configured to transmit a signal to the control circuit. Thecontrol circuit is configured to identify one or more steps of a patientusing the motion sensing device signal.

In Example 2, the motion sensing device of Example 1 optionally includesan accelerometer.

In Example 3, the systems of Examples 1-2 optionally include a telemetrycircuit, the telemetry circuit coupled to the control circuit forcommunicating to an external device.

In Example 4, the systems of Examples 1-3 optionally include theexternal device, wherein the external device is a local external device;and further wherein the local external device is configured tocommunicate with a remote external device.

In Example 5, at least one of the implantable medical device and theexternal device of Examples 1-4 are optionally configured to calculate,using data about the one or more steps of the patient, at least one of acount of the one or more steps of the patient, a count of the one ormore steps of the patient during a particular period of time, a physicalactivity category, a distance traveled by the patient during aparticular period of time, an amount of time spent walking by thepatient during a particular period of time, a caloric expenditure by thepatient during a particular period of time, an amount of time betweenepisodes of walking, a stride pattern of the patient, a measure ofactivity of the patient, a velocity of the patient, a length of aparticular step, and an amount of time relating to a duration of theparticular step.

In Example 6, the systems of Examples 1-5 optionally include anelectrical stimulation circuit coupled to the control circuit, theelectrical stimulation circuit configured to deliver at least oneelectrical pulse using data about the one or more steps of the patient.

In Example 7, the data about the one or more steps of the patient ofExamples 1-6 are optionally used to initiate or adjust at least one ofan AV delay, a current pacing rate, a baseline pacing rate, an upperlimit of a pacing rate, and an acceleration of a pacing rate.

In Example 8, the control circuit of Examples 1-7 is optionallyconfigured to confirm a single step by identifying a first step followedby a second step within a particular period of time.

In Example 9, the control circuit of Examples 1-8 is optionallyconfigured to confirm a single step by identifying three consecutivesteps.

In Example 10, the accelerometer of Examples 1-9 optionally includes athree axis accelerometer, and the control circuit is optionallyconfigured to identify a step up by the patient, a step down by thepatient, and a step forward by the patient.

In Example 11, the systems of Examples 1-10 optionally include a drugtitration circuit, the drug titration circuit configured to deliver adrug using data about the one or more steps of the patient.

In Example 12, the systems of Examples 1-11 optionally include an alertcircuit coupled to the control circuit, the alert circuit configured toprovide an alert using data about the one or more steps of the patient.

In Example 13, the control circuit of Examples 1-12 optionally include acircuit to identify the one or more steps of the patient by one or moreof identifying a peak in an output of the accelerometer and by patternmatching an output of the accelerometer.

In Example 14, a process includes receiving data from an implantablemotion sensing device, and processing the data to identify one or moresteps taken by a patient.

In Example 15, the motion sensing device of Example 14 optionallyincludes an accelerometer.

In Example 16, the processes of Examples 14-15 optionally includetransmitting the data from the implantable motion sensing device to anexternal device, and displaying the data about the one or more stepstaken by the patient on the external device.

In Example 17, the processes of Examples 14-16 optionally includetransmitting the data about the one or more steps taken by the patientto an external device, and displaying the data about the one or moresteps taken by the patient on the external device. The processing thedata to identify the one or more steps taken by the patient optionallyoccurs on the external device.

In Example 18, the processes of Examples 14-17 optionally include usingthe data about the one or more steps taken by the patient to calculateat least one of a number of steps taken by the patient, a number ofsteps taken by the patient during a particular time period, a physicalactivity category, a caloric expenditure by the patient, a stridepattern of the patient, a measure of activity of the patient, a velocityof the patient, a length of a time interval between episodes of walkingby the patient, a time duration of an episode of walking of the patient,a distance covered by the patient, a measure of sustained steps during aperiod of time, and a gait of the patient.

In Example 19, the processes of Examples 14-18 optionally includeidentifying a step by identifying three or more consecutive steps.

In Example 20, the processes of Examples 14-19 optionally includeidentifying a step by identifying a first step followed by a second stepwithin a particular period of time.

In Example 21, the processes of Examples 14-20 optionally include adisease progression of a patient using the data about the one or moresteps taken by the patient.

In Example 22, the processes of Examples 14-21 optionally includegenerating an alert using the data about the one or more steps taken bythe patient.

In Example 23, the processes of Examples 14-22 optionally includealtering an operation of an implantable medical device using the dataabout the one or more steps taken by the patient.

In Example 24, the processes of Examples 14-23 optionally includeidentifying the data about the one or more steps taken by the patient byone or more of identifying a peak in an output of the accelerometer andby pattern matching the output of the accelerometer.

In Example 25, the processes of Examples 14-24 optionally includecategorizing a patient into a physical activity category using the dataabout the one or more steps taken by the patient.

In Example 26, the processes of Examples 14-25 optionally includeidentifying a first step, starting a timer, and inhibiting anidentification of a second step until after expiration of the timer.

In Example 27, the processes of Examples 14-26 optionally includeevaluating patient compliance using the data about the one or more stepstaken by the patient.

In Example 28, the patient compliance of Examples 14-27 optionallyrelates to a patient exercise program.

In Example 29, the processes of Examples 14-28 optionally includeidentifying a step up by the patient, a step down by the patient, and astep forward by the patient.

In Example 30, a system includes an implantable medical device, theimplantable medical device including a control circuit, a motion sensingdevice, coupled to the control circuit, the motion sensing deviceconfigured to transmit a signal to the control circuit, and a telemetrycircuit, coupled to the control circuit, and configured to transmit asignal to an external device. The external device is configured toidentify one or more steps of a patient using the signal from theimplantable medical device.

In Example 31, the system of Example 30 optionally includes the externaldevice.

In Example 32, the motion sensing device of Examples 30-31 optionallyincludes an accelerometer.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe substantially similar components in different views Likenumerals having different letter suffixes may represent differentinstances of substantially similar components. The drawings illustrategenerally, by way of example, but not by way of limitation, variousexamples discussed in the present document.

FIG. 1 illustrates an example of an implanted medical device incommunication with an external device via a telemetry system.

FIG. 2 illustrates an example of a block diagram of an implantablemedical device.

FIG. 3 illustrates an example output of an accelerometer.

FIG. 4 illustrates an example flowchart of a process to identify stepsof a patient using an implantable medical device.

FIG. 5 illustrates several measurements that can be calculated usingpatient step data.

FIG. 6 illustrates several methods to verify an actual patient step.

FIG. 7 illustrates several actions that can be taken using patient stepdata.

DETAILED DESCRIPTION

The following detailed description includes references to theaccompanying drawings, which form a part of the detailed description.The drawings show, by way of illustration, specific embodiments in whichthe invention may be practiced. These embodiments are also referred toherein as “examples.” The embodiments may be combined, other embodimentsmay be utilized, or structural, logical and electrical changes may bemade without departing from the scope of the present invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims and their equivalents.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherusages of “at least one” or “one or more.” In this document, the term“or” is used to refer to a nonexclusive or, such that “A or B” includes“A but not B,” “B but not A,” and “A and B,” unless otherwise indicated.Furthermore, all publications, patents, and patent documents referred toin this document are incorporated by reference herein in their entirety,as though individually incorporated by reference. In the event ofinconsistent usages between this document and those documents soincorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

FIG. 1 is a diagram illustrating an example of a medical device system100, and portions of an environment in which it is used. The environmentincludes a body 102 with a heart 105. System 100 includes an implantablemedical device 110, a lead system 108, a first adjunct device orexternal system 170, a second adjunct device or external system 180, anda wireless telemetry link 160. The first external system 170 can bereferred to as a local external system, and the second external system180 can be referred to as a remote external system. Heart rate data,pacing data, EGM data, motion sensing device data (e.g., accelerometerdata), and other data can be transferred from the device 110 to theexternal system 170 via the telemetry link 160. The telemetered dataloaded into the device 170 can then be used for analysis andinterpretation either immediately or at a later time.

FIG. 2 illustrates an example of the implantable medical device 110 ofFIG. 1. The device 110 includes a control circuit 210 and anaccelerometer 220. While FIG. 2 illustrates an example device 110 asincluding an accelerometer, other motion sensing devices such as amercury switch could also be used. In systems in which an accelerometeris present, the accelerometer could be a 1-axis, 2-axis, or 3-axisaccelerometer. For ease of explanation, examples of the device 110described herein will be described as having an accelerometer.

In an example, an anti-aliasing or other filter 230 is located betweenthe control circuit 210 and the accelerometer 220. An amplifier couldalso be placed between the control circuit 210 and the accelerometer220. A telemetry circuit 240, a memory circuit 250, an electricalstimulation circuit 260, a drug titration circuit 270, or an alertcircuit 280 can be connected to the control circuit 210.

The memory circuit 250 can be configured to store data about the one ormore steps of a patient. The data can include an accelerometer trace asillustrated in FIG. 3. The accelerometer trace 300 includes informationsuch as the amplitude of a peak associated with a step (such anamplitude is normally less for a step up than a normal step or a stepdown), an interval between steps, and a duration of a step.

In an example system, the implantable medical device 110 can be acardiac rhythm management device. In another example system, thetelemetry circuit 240 can be configured to communicate with the externalsystem 170. The external system 170 can be a local external system. Thelocal external system can be attachable to a patient's body, or it canbe a system that is separate from a patient's body. The external devicecan also be a remote external device, such as a device to which apatient's physician can have access. In a system with a remote externaldevice, a local external device is configured to communicate with theremote external device.

FIG. 3 illustrates an example trace 300 of an implantable accelerometeroutput generated by a patient walking on a treadmill at a speed ofapproximately 2 mph. The trace 300 includes several peaks (valleys) ordepressions 310 that are caused by the patient's foot coming in contactwith the treadmill surface during the test. These depressions 310 can bereferred to as footfalls, and the control circuit can be configured toidentify the depressions 310, and consequently identify each step that apatient takes. This identification of the depressions 310 can be afunction of amplitude, morphology, or a combination of amplitude andmorphology. This analysis of the depressions 310 can be performed in thecontrol circuit 210, the external device 170, or the external device180.

FIG. 4 illustrates an example flowchart of a process 400 to identifysteps of a patient using an implantable medical device such as theimplantable medical device 110 of FIG. 2. The operations illustrated inFIG. 4 need not all be executed in each example implantable medicaldevice system, and the operations need not be executed in the order asillustrated in FIG. 4. At 405, data is received from an implantablemotion sensing device, such as an implantable accelerometer. At 410,candidate patient steps are identified. At 415, the identified candidatesteps are confirmed as actual patient steps. At 420, a step isclassified. For example, a step can be classified as a step up, a stepdown, or a step forward.

The data about the one or more steps taken by the patient are used tocalculate several measures associated with the patient. FIG. 5illustrates that these measures can include a number of steps taken bythe patient during a particular time period (505), a total number ofsteps taken by the patient without regard to a time period (510), aclassification of the patient based on the number of steps taken by thepatient (515), a caloric expenditure of the patient (520), a stridepattern of the patient (525), a measure of activity of the patient(530), a velocity of the patient (540), a length of a time intervalbetween episodes of walking by the patient (545), a time duration of anepisode of walking by the patient (550), a distance covered by thepatient (560), a measure of sustained steps during a period of time(565), and a gait of the patient (570). At 575, a three-axisaccelerometer 220 in an implantable medical device 110 can identify astep up by the patient, a step down by the patient, and a step forwardby the patient. Such data can be used by a physician to monitor patientcompliance, general health status of a patient, or the progression orregression of a diseased patient.

As indicated above, a patient can be classified into a group based onthe number of steps that that patient takes during a day. In an example,the group includes a physical activity category. One such classificationsystem has been developed by the New York Heart Association (NYHA). Asimilar system could be developed based on the number of steps that apatient takes in a day. For example, a patient who takes more than10,000 steps per day could be identified as a class I patient. A class Ipatient may not be limited in any activities, and may suffer no symptomsfrom ordinary activities. A patient who takes between 5,000 and 7,000steps per day could be identified as a class II patient. A class IIpatient may be mildly limited in activities, and may be comfortable withrest or mild exertion. A patient who takes between 3,000 and 5,000 stepsper day could be identified as a class III patient. A class III patientmay experience a marked limitation of activity, and a class III patientmay only be comfortable when at rest. A patient who takes less than1,000 steps per day could be identified as a class IV patient. A classIV patient should be at complete rest in a bed or a chair. Any physicalactivity may bring on discomfort for a class IV patient, and symptomsmay occur in a class IV patient at rest.

The caloric expenditure can be calculated by first using the number ofsteps taken by a patient to determine the distance traveled by thepatient, and then using the weight of the patient, calculating thecaloric expenditure of the patient by one of several methods known inthe art. In an example system, a change in the gait or stride pattern ofa patient can be noted by saving data relating to the stride or gait ofa patient in the memory circuit 250, such as the average time betweenfootfalls, and thereafter comparing current stride and gait data withthe patient's historical data. In another example system, the length ofthe patient's stride can be calculated and recalculated based on thetime between footfalls.

FIG. 6 illustrates that the control circuit 210, the external system170, or the external system 180 can execute one or more of severalprocedures that help assure that only steps of a patient are identified(and not some other activity, disturbance, or noise), and that a step iscounted only once. In one example, at 610, a step is identified as astep when the control circuit 210, the external system 170, or theexternal system 180 identifies three or more consecutive steps. This canbe accomplished by identifying three consecutive depressions 310 in FIG.3 within a time frame wherein a patient would take three consecutivesteps. If three depressions 310 are not identified in that time frame,then data in that time frame is not identified as a step. In anotherexample, at 620, the control circuit 210, the external system 170, orthe external system 180 identifies a step by identifying a first stepthat is followed by a second step within a particular period of time.The period of time can be set on a patient by patient basis by testingthe patient and determining the average time between footfalls of thepatient during normal walking of the patient.

In another example system, at 630, the control circuit 210, the externalsystem 170, or the external system 180 identifies a first step (via thedetection of a depression 310 (i.e., a footfall)), starts a timer, andthen inhibits the identification of a second step until after expirationof the timer. The timer can be a dynamic timer, such that as the pace ofa patient's walking increases, the timer window is shortened tocompensate for the increased walking pace. The use of a timer in thismanner prevents counting a single step as more than one step, orinterpreting noise in the system as a step.

FIG. 7 illustrates several functions that an implantable medical devicecan implement using patient step data. At 710, a disease progression ofa patient can be monitored using the data about the one or more stepstaken by the patient. For example, if the number of steps taken by apatient per day decreases over a period of time, that can be indicativeof a worsening of the patient's condition. In connection with theworsening of the patient's condition, it can also be noted whether apatient has moved from one physical activity category to anotherphysical activity category.

At 720, the alert circuit 280, the external system 170, or the externalsystem 180 can generate an alert using the data about the one or moresteps taken by the patient. This alert can be for the benefit of thepatient to inform that patient that he is either hyperactive for hisparticular condition, hypoactive for his particular condition, or as anindication that his condition is worsening. The alert can also be forthe benefit of the patient's physician, and can serve as generalinformation regarding how the patient is progressing or digressing, orcan indicate a more dire situation such a substantial decrease in thepatient's number of steps taken over a time period indicating aworsening of the patient's condition. At 730, a physician or otherhealth care provider can use the patient step data to evaluate patientcompliance. For example, if a patient has been instructed to exercise bywalking a certain distance per day, or the patient has been instructedto rest and recover, the patient's compliance with those instructionscan be determined at the external system 170 or the external system 180using the patient step data.

At 740, the control circuit 210 alters an operation of the implantablemedical device 110 using the data about the one or more steps taken bythe patient. For example, if the implantable medical device 110 is acardiac rhythm management device having an electrical stimulationcircuit 260, the control circuit 210 could alter an AV delay, a currentpacing rate, a baseline pacing rate, an upper limit of the pacing rate(by lowering it or raising it in response to the patient step data), oran acceleration of the current pacing rate. As another example, at 750,if the implantable medical device 110 includes a drug delivery circuit270, an operation of the drug delivery circuit could be altered by thecontrol circuit 210 using the patient step data. If the drug deliverycircuit 270 delivers insulin to the patient, the rate or level ofinsulin delivery can be modified based using the patient step data. Forexample, if a patient is taking more steps over a particular period oftime than is normal for that patient, the drug delivery circuit 270 canincrease the rate or level of insulin delivery in response to theincrease in steps taken by the patient.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described embodiments (or one ormore aspects thereof) can be used in combination with each other. Otherembodiments will be apparent to those of skill in the art upon reviewingthe above description. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled. In the appendedclaims, the terms “including” and “in which” are used as theplain-English equivalents of the respective terms “comprising” and“wherein.” Also, in the following claims, the terms “including” and“comprising” are open-ended, that is, a system, device, article, orprocess that includes elements in addition to those listed after such aterm in a claim are still deemed to fall within the scope of that claim.Moreover, in the following claims, the terms “first,” “second,” and“third,” etc. are used merely as labels, and are not intended to imposenumerical requirements on their objects.

The Abstract is provided to comply with 37 C.F.R. §1.72(b), whichrequires that it allow the reader to quickly ascertain the nature of thetechnical disclosure. It is submitted with the understanding that itwill not be used to interpret or limit the scope or meaning of theclaims. Also, in the above Detailed Description, various features may begrouped together to streamline the disclosure. This should not beinterpreted as intending that an unclaimed disclosed feature isessential to any claim. Rather, inventive subject matter may lie in lessthan all features of a particular disclosed embodiment. Thus, thefollowing claims are hereby incorporated into the Detailed Description,with each claim standing on its own as a separate embodiment.

1. A system comprising: an implantable cardiac rhythm management devicecomprising: a control circuit; and a motion sensing device coupled tothe control circuit, the motion sensing device configured to transmit asignal to the control circuit; wherein the control circuit is configuredto: identify a candidate step of a patient using the motion sensingdevice signal; and confirm that the candidate step is an actualindividual step of the patient.
 2. The system of claim 1, wherein themotion sensing device includes an accelerometer.
 3. The system of claim2, wherein the accelerometer comprises a three-axis accelerometer, andwherein the control circuit is configured to classify the actualindividual step as one of a step up by the patient, a step down by thepatient, and a step forward by the patient.
 4. The system of claim 2,wherein the control circuit comprises a circuit to identify one or moreactual individual steps of the patient by one or more of identifying apeak in an output of the accelerometer and by pattern matching an outputof the accelerometer.
 5. The system of claim 1, comprising an externaldevice communicatively coupled to the implantable cardiac rhythmmanagement device.
 6. The system of claim 5, wherein the external deviceis a local external device configured to communicate with a remoteexternal device.
 7. The system of claim 5, wherein at least one of theimplantable cardiac rhythm management device and the external device areconfigured to determine, using data from one or more actual individualsteps of the patient, at least one of: a count of the one or more stepsof the patient; a count of the one or more steps of the patient during aparticular period of time; a physical activity category; a distancetraveled by the patient during a particular period of time; an amount oftime spent walking by the patient during a particular period of time; acaloric expenditure by the patient during a particular period of time;an amount of time between episodes of walking; a stride pattern of thepatient; a measure of activity of the patient; a velocity of thepatient; a length of a particular step; and an amount of time relatingto a duration of the particular step.
 8. The system of claim 1,comprising an electrical stimulation circuit coupled to the controlcircuit, the electrical stimulation circuit configured to deliver anelectrical pulse, wherein delivery of the electrical pulse is based ondata from one or more actual individual steps of the patient.
 9. Thesystem of claim 1, wherein the control circuit is configured to confirmthat the candidate step is an actual individual step of the patient byidentifying a first step followed by a second step within a particularperiod of time.
 10. The system of claim 1, wherein the control circuitis configured to confirm that the candidate step is an actual individualstep of the patient by identifying three consecutive steps.
 11. A methodcomprising: receiving data from an implantable motion sensing deviceassociated with an implantable cardiac rhythm management device; andprocessing the data to: identify a candidate step taken by a patient;and confirm that the candidate step is an actual individual step of thepatient.
 12. The method of claim 11, comprising classifying the actualindividual step as one of a step up by the patient, a step down by thepatient, and a step forward by the patient using the data from theimplantable motion sensing device, wherein the implantable motionsensing device includes an accelerometer.
 13. The method of claim 11,wherein processing the data includes identifying one or more actualindividual steps of the patient by one or more of identifying a peak inan output of an accelerometer of the implantable motion sensing deviceand by pattern matching an output of the accelerometer.
 14. The methodof claim 11, comprising: transmitting the data from the implantablemotion sensing device to an external device; and displaying the dataabout the one or more steps taken by the patient on the external device.15. The method of claim 11, comprising using data about one or moreactual individual steps taken by the patient to determine at least oneof: a number of steps taken by the patient; a number of steps taken bythe patient during a particular time period; a physical activitycategory; a caloric expenditure by the patient; a stride pattern of thepatient; a measure of activity of the patient; a velocity of thepatient; a length of a time interval between episodes of walking by thepatient; a time duration of an episode of walking of the patient; adistance covered by the patient; a measure of sustained steps during aperiod of time; and a gait of the patient.
 16. The method of claim 11,wherein processing the data includes confirming that the candidate stepis an actual individual step by identifying three or more consecutivesteps.
 17. The method of claim 11, wherein processing the data includesconfirming that the candidate step is an actual individual step byidentifying a first step followed by a second step within a particularperiod of time.
 18. A system comprising: an implantable cardiac rhythmmanagement device comprising: a control circuit; a motion sensing devicecoupled to the control circuit, the motion sensing device configured totransmit a signal to the control circuit; and a telemetry circuit,coupled to the control circuit, and configured to transmit a signal toan external device; wherein the external device is configured to;identify a candidate step of a patient using the motion sensing devicesignal; and confirm that the candidate step is an actual individual stepof the patient.
 19. The system of claim 18, wherein the external deviceis configured to confirm that the candidate step is an actual individualstep of the patient by identifying a first step followed by a secondstep within a particular period of time.
 20. The system of claim 18,wherein the external device is configured to confirm that the candidatestep is an actual individual step of the patient by identifying threeconsecutive steps.